The prior art for non-emissive displays, particularly liquid crystal displays, include either reflective displays or surface light source (transmissive) displays, commonly denoted backlit displays. The conventional reflective display which uses a reflective film as the bottom layer to redirect ambient light back through the display elements has a composition as illustrated in FIG. 1. In this drawing ambient light 10 (sunlight, artificial light—such as office lighting—or from a light source 11 attached to the top of the unit) enters the display unit, passes through the various layers of the unit, 6 polarizers, 7 glass plates (which may include color filters, common electrodes, TFT matrix, or other components), and 8 liquid crystal suspension, and is redirected from the reflective film 9 back through the various layers to produce an image. This method of creating an image with available ambient light is limited by the available light. This method is not an effective means for producing high quality graphic images and severely limits the quality of color images in a variety of conditions. The conventional backlit (transmissive) display has a composition as illustrated in FIG. 2. In this drawing, light is produced with a backlight assembly 12 and directed as light ray 13, through the various layers, such as 6 polarizers, 7 glass plates (which may include color filters, common electrodes, TFT matrix, or other components), and 8 liquid crystal suspension, to produce an image.
Previous attempts to use simultaneously the ambient light and a backlight have resulted in applications that compromise both the transmissive qualities and the reflective qualities of the display. Hochstrate, in U.S. Pat. No. 4,196,973 teaches the use of a transflector for this purpose. Weber, in U.S. Pat. No. 5,686,979, col. 2, teaches the limitations of the transflector for this purpose and alternatively proposes a switchable window that at one time is wholly transmissive and at another time is wholly reflective.